1. Field of the Invention
This invention relates generally to plastic boats and to a method for making the same. More specifically, the invention relates to boats made of a molded polystyrene unitary core with molded, high strength plastic inner and outer skins.
2. Description of the Prior Art
A large number of products are made which have a plastic foam core and a skin or shell made of a higher density plastic. This type of structure has been particularly attractive in products which require good thermal or sound insulating properties. Ice chests are a good example of such products.
The foamed core/plastic skin structure has also been attractive in products where light weight or safety is desired. Safety is a factor, for example, in items such as cosmetic jars where glass and ceramics have proven to be quite frangible.
While the foamed core/plastic skin structure has a number of desirable properties, the structure thus far has been limited to products which are relatively small, such as surfboards. The structure, however, would be very attractive in work boats and other large boats because of its light weight, strength, and low production and material costs. Unfortunately, attempts to adapt the structure to such large-size products have met with discouraging results.
These attempts, for the most part, have involved the use of the well-known technique of forming a foamed polyurethane core, in place, between an inner plastic skin and an outer plastic skin. Liquid polyurethane is injected, by methods such as spraying or pouring, into the volume defined by the inner and outer skins and then foamed in place. The technique is relatively simple, but it has proven to have serious shortcomings when making large products, such as work boats.
In particular, it has been found that the polyurethane core frequently continues to expand with time, thereby causing the products to take on a lumpy appearance. These problems have limited the application of the foam core/plastic skin structure to large products. This has been especially unfortunate for the boat industry, because the good properties of the structure are especially applicable to large boats. It is this very application that the present invention now makes possible.
Other attempts have been made to manufacture boats using a molded plastic shell filled with a multiple piece core. Such a boat is disclosed in U.S. Pat. No. 3,611,461 to Wurzberger. A multi-piece core does not offer the same structural integrity as a unitary core, and is therefore less suited to carrying the heavier loads associated with large work boats. The present invention is directed towards a large work boat consisting of a unitary core such that it will possess the necessary structural integrity to carry the loads normally carried by large work boats.